JP 2-136818 (A) discloses a display device for projecting an image onto a retina of a viewer or wearer of a device which is illustrated in FIG. 13. The display device has an optical system generally indicated by reference numeral 30. The optical system 30, which is supported by a frame in front of an eye 31 of the wearer, has a plurality of components aligned toward the eye 31 of the wearer, i.e., a point source (light source) 32, an image plate made of a transmitting liquid crystal display (LCD) panel 33 and an eyepiece 34 or lens.
With this arrangement, light emitted from the point source 32 is transmitted through the LCD panel 33. An image formed by light transmitted through the LCD panel 33 is focused by the eyepiece 34 on the pupil 35 and then transmitted through the crystalline lens 36 and the vitreous body 37 onto the retina 38. As described above, the display device is designed so that the point source 32 is focused on the pupil 35, which results in a good directivity of light. Also, even the myoptic and hyperoptic person 31 can view the image displayed on the LCD panel 33 clearly. However, even a slight movement of his or her eye causes his or her iris to shut the incident light and thereby disables him or her from seeing the image. For example, an average diameter of the adult pupil in a dark place is about 7 mm. Then, a movement of the pupil of about ±3.5 mm or more disables the wearer from seeing the image. In a lighted place, the average diameter is reduced to about 4 mm. Therefore, movement of the pupil of about ±2.0 mm or more disables the wearer to see the image.
Another display device has been proposed so far in which a panel-like light source is positioned in close contact with the LCD panel. However, this arrangement is disadvantageous to the display device that the wearer wears it in front of his or her eyes because a sufficient space could not be obtained between the panel-like light source and the LCD due to its compactness requirement. This in turn results in that light transmitted through the LCD panel is reflected in all directions and therefore non-directive light is projected into the pupil of the wearer. This requires the wearer to correct an aberration of the optics which project light into the pupil, which significantly complicates the structure of the optics. Also, the lens of the wearer is required to focus the projected image into his or her retina. However, the distance between the LCD and the pupil is so limited that the wearer with weak eyes needs to wear glasses. Also, moving eyes away from the liquid panel to see natural scenes causes light transmitted through the LCD panel to enter the pupil of the wearer, which results in considerable difficulties in viewing the natural scenes.
In order to solve those problems, another display device is disclosed in JP 8-211325 (A), which includes a panel-like light source in which a number of point sources are aligned in two directional directions. This arrangement, however, is complicated in structure and therefore it is difficult to minimize the device.